The present invention relates to electronic displays, and in particular to non-emissive, flat-panel displays.
Electrooptic display systems typically include an electrooptic element (e.g., the display material itself) and electrodes (either opaque or transparent) for applying control voltages to the electrooptic element. Such a system may also include a nonlinear element to allow for multiplexing of the address lines to the electrodes, and an insulating material between various layers of the display system. These components have been fabricated by a multitude of conventional processes. For versatility and convenience of manufacture, many recent efforts have focused on producing all components of such displays by deposition printing using, for example, screen or ink-jet printing apparatus. The use of printing techniques allows displays to be fabricated on a variety of substrates at low cost.
The conducting materials used for electrodes in display devices have traditionally been manufactured by commercial deposition processes such as etching, evaporation, and sputtering onto a substrate. In electronic displays it is often necessary to utilize a transparent electrode to ensure that the display material can be viewed. Indium tin oxide (ITO), deposited by means of a vacuum-deposition or sputtering process, has found-widespread acceptance for this purpose. More recently, ITO inks have been deposited using a printing process (see, e.g., U.S. Pat. No. 5,421,926).
For rear electrodes (i.e., the electrodes other than those through which the display is viewed) it is often not necessary to utilize transparent conductors. Such electrodes can therefore be formed from a material such as a silver ink. Again, these materials have traditionally been applied using costly sputtering or vacuum deposition methods.
Nonlinear elements, which facilitate matrix addressing, are an essential part of many display systems. For a display of Mxc3x97N pixels, it is desirable to use a multiplexed addressing scheme whereby M column electrodes and N row electrodes are patterned orthogonally with respect to each other. Such a scheme requires only M+N address lines (as opposed to Mxc3x97N lines for a direct-address system requiring a separate address line for each pixel). The use of matrix addressing results in significant savings in terms of power consumption and cost of manufacture. As a practical matter, its feasibility usually hinges upon the presence of a nonlinearity in an associated device. The nonlinearity eliminates crosstalk between electrodes and provides a thresholding function. A traditional way of introducing nonlinearity into displays has been to use a backplane having components that exhibit a nonlinear current/voltage relationship. Examples of such devices used in displays include thin-film transistors (TFT) and metal-insulator-metal (MIM) diodes. While these types of devices achieve the desired result, both involve thin-film processes. Thus they suffer from high production cost as well as relatively poor manufacturing yields.
Another nonlinear system, which has been used in conjunction with liquid crystal displays, a printed varistor backplane (see, e.g., U.S. Pat. Nos. 5,070,326; 5,066,105; 5,250,932; and 5,128,785, hereafter the xe2x80x9cYoshimoto patents,xe2x80x9d the entire disclosures of which are hereby incorporated by reference). A varistor is a device having a nonlinear current/voltage relationship. Ordinarily, varistors are produced by pressing various metal-oxide powders followed by sintering. The resulting material can be pulverized into particulate matter, which can then be dispersed in a binder.
Additionally, the prior art mentions the use of a varistor backplane to provide thresholding for a non-emissive electrophoretic display device; see Chiang, xe2x80x9cA High Speed Electrophoretic Matrix Display,xe2x80x9d SID 1980 Technical Digest. The disclosed approach requires the deposition of the display material into an evacuated cavity on a substrate-borne, nonprinted varistor wafer. Thus, fabrication is relatively complex and costly.
Some success has been achieved in fabricating electronic displays using printing processes exclusively. These displays, however, have for the most part been emissive in nature (such as electroluminescent displays). As is well known, emissive displays exhibit high power-consumption levels. Efforts devoted to nonemissive displays generally have not provided for thresholding to facilitate matrix addressing.
The present invention facilitates fabrication of an entire nonemissive (reflective), electronically addressable display using printing techniques. In particular, printing processes can be used to deposit the electrodes, insulating material, the display itself, and an array of nonlinear devices to facilitate addressing. Accordingly, fabrication of the displays of the present invention may be accomplished at significantly lower cost and with far less complexity than would obtain using coventional fabrication technologies. Furthermore, the approach of the present invention affords greater versatility in fabrication, allowing the displays to be applied to substrates of arbitrary flexibility and thickness (ranging, for example, from polymeric materials to paper). For example, static screen-printed displays may be used in signs or lettering on consumer products; the invention can also be used to form dynamic, electronically alterable displays. Moreover, the invention can be employed to produce flat-panel displays at manufacturing costs well below those associated with traditional devices (e.g., liquid crystal displays).
As used herein, the term xe2x80x9cprintingxe2x80x9d connotes a non-vacuum deposition process capable of creating a pattern. Examples include screen printing, ink-jet printing, and contact processes such as lithographic and gravure printing.
For the display element, the present invention utilizes certain particle-based nonemissive systems such as encapsulated electrophoretic displays (in which particles migrate within a dielectric fluid under the influence of an electric field), electrically or magnetically driven rotating-ball displays (see, e.g., U.S. Pat. Nos. 5,604,027 and 4,419,383), and encapsulated displays based on micromagnetic or electrostatic particles (see, e.g., U.S. Pat. Nos. 4,211,668; 5,057,363 and 3,683,382). A preferred approach is based on discrete, microencapsulated electrophoretic elements, suitable examples of which are disclosed in U.S. application Ser. No. 08/738,260 and PCT application Ser. No. US 96/13469. The entire disclosures of the ""027, ""383, ""668, ""363, and ""382 patents, as well as the ""260 and ""469 applications, are hereby incorporated by reference.
Electrophoretic displays in accordance with the ""260 application are based on microcapsules each having therein an electrophoretic composition of a dielectric fluid and a suspension of particles that visually contrast with the dielectric liquid and also exhibit surface charges. A pair of electrodes, at least one of which is visually transparent, covers opposite sides of a two-dimensional arrangement of such microcapsules. A potential difference between the two electrodes causes the particles to migrate toward one of the electrodes, thereby altering what is seen through the transparent electrode. When attracted to this electrode, the particles are visible and their color predominates; when they are attracted to the opposite electrode, however, the particles are obscured by the dielectric liquid.
In accordance with the present invention, the electrophoretic microcapsules are suspended in a carrier material that may be deposited using a printing process. The suspension thereby functions as a printable electrophoretic ink. Preferably, the electrodes are also applied using a printing process. For example, the transparent electrode(s) may be a print-deposited ITO composition, as described in the above-mentioned ""926 patent, and the rear electrodes may also be an ITO composition or, alternatively, a silver ink. The electrophoretic ink is deposited between the electrode arrays, forming a sandwich structure.
Preferably, the invention also includes a series of nonlinear devices that facilitate matrix addressing, whereby Mxc3x97N pixels are address with M+N electrodes; again, these devices (which may include diodes, transistors, varistors or some combination) are desirably applied by printing. In one approach, a varistor backplane is deposited in accordance with, for example, the Yoshimoto patents described above. Alternatively, a backplane of nonlinear devices may utilize printed particulate silicon diodes as taught, for example, in U.S. Pat. No. 4,947,219 (the entire disclosure of which is hereby incorporated by reference). With this approach, a particulate doped silicon is dispersed in a binder and applied in layers to produce diode structures.
Thus, a display system in-accordance with the invention may include a substrate upon which the display system is fabricated; a printable electrooptic display material, such as a microencapsulated electrophoretic suspension; printable electrodes (typically based on a transparent, conductive ink) arranged in an intersecting pattern to allow specific elements or regions of the display material to be addressed; insulating layers, as necessary, deposited by printing; and an array of nonlinear elements that facilitate matrix addressing. The nonlinear devices may include printed, particulate Schottky diodes, particulate PN diodes, particulate varistor material, silicon films formed by chemical reduction, or polymer semiconductor films.
The displays of the present invention exhibit low power consumption, and are economically fabricated. If a bistable display material is used, refreshing of the display is not required and further power consumption is achieved. Because all of the components of the display are printed, it is possible to create flat-panel displays on very thin and flexible substrates.
In another aspect, the invention comprises means for remotely powering a nonemissive display, and in still another aspect, the invention comprises a graduated scale comprising a series of nonemissive displays each associated with a nonlinear element having a different breakdown voltage.